Added initial pipes, saga, error handling and retry strategy

- Added IErrorHandler interface to support custom error handling.
Returning true in the implementation prevents any errors to be bubbled up, and prevents any following handlers to be executed.

- Added IPipeBuilder interface to support a custom message pipeline

- Made the AutofacDispatcher pipeline pluggable using IPipeBuilder and IErrorHandler
OnAfterConsume actions are always executed in reverse order, and executed even if an error has occured to allow any cleanup

- Added initial version of the SimpleSagaPipe to support (very basic) saga's

- Refactored the IRepository<TState, TCorrelationId> so it only has to implement the asynchronous methods

- Added TimeSpanExtensions for friendly TimeSpan formatting

- Added initial retry strategy